1. Field of the Invention
The present invention relates to an image drawing apparatus that can execute transmission drawing processing when performing a bit block transfer operation with respect to image data stored in an arbitrary rectangular area (or a block area) of a memory device.
2. Description of the Related Art
Conventionally, when performing a bit block transfer (hereinafter called BITBLT transfer) operation with respect to image data stored in an arbitrary block area of a memory device, the use of transmission drawing processing has hardly been considered. If the transmission drawing processing is executed when performing the BITBLT transfer operation, or the bit block copying of a rectangular-block image from the source to the destination, the source image becomes transparent. Even after the copying it is possible to distinguish the destination image which lies originally at the destination to some extent because of the transparency of the transferred image. Hence, the transmission drawing processing makes the renewal of image data at the destination easily discriminable.
There is a conventional image drawing apparatus that is able to execute the transmission drawing processing. However, in such conventional image drawing apparatus, even if the transmission drawing processing is performed, the transmission coefficient for every pixel of image data stored in a block area of a memory device serve as a fixed value. The BITBLT transfer operation is performed merely with such fixed transmission coefficients.
A description will be given of examples of the transmission drawing processing which is performed by a conventional image drawing apparatus with reference to FIG. 1A and FIG. 1B. For the sake of convenience of description, a change of the corresponding image on the screen of a display device after the BITBLT transfer operation is performed is shown in FIG. 1A and FIG. 1B.
FIG. 1A shows an example of the BITBLT transfer operation that is performed in order to bit-block copy the image from the source to the destination. In the example of FIG. 1A, the transmission drawing processing is not performed. FIG. 1B shows another example of the transmission drawing processing which is executed when the BITBLT transfer operation is performed with the transmission coefficient for every pixel of the image that is set to a fixed value. As in the example of FIG. 1B, the conventional image drawing apparatus executes the transmission drawing processing in which the BITBLT transfer operation is performed with the transmission coefficient for every pixel of the image stored in a block area of a memory device that is set to a fixed value. The effect of the transmission drawing processing by the conventional image drawing apparatus is limited as shown in FIG. 1B, and it is impossible to execute the transmission drawing processing in which the BITBLT transfer operation is performed while the transmission coefficient is arbitrarily varied for every pixel of the image.
Next, a description will be given of examples of the desired transmission drawing processing in which the BITBLT transfer operation is performed while the transmission coefficient is arbitrarily varied for every pixel of the image, with reference to FIG. 2A and FIG. 2B. For the sake of convenience of description, a change of the corresponding image on the screen of a display device after the BITBLT transfer operation is performed is shown in FIG. 2A and FIG. 2B.
FIG. 2A shows an example of the desired transmission drawing processing. In the example of FIG. 2A, when the BITBLT transfer operation is performed in order to copy a rectangular-block image from the source to the destination, the transmission coefficient is decreased in a diagonal direction from the lower left corner of the block (the image) to the center and increased in a diagonal direction from the center to the upper right corner of the block.
FIG. 2B shows another example of the desired transmission drawing processing. In the example of FIG. 2B, when the BITBLT transfer operation is performed in order to copy a rectangular-block image from the source to the destination, the transmission coefficient is increased in radial directions from the center of the block (the image) to the circumferential portions of the block.
Generally, a very long processing time is required when the BITBLT transfer operation is performed while the transmission coefficient is varied for every pixel of the image stored in a block area (or a rectangular region) of a memory device, regardless of whether the changing ratio of the transmission coefficient is linear or nonlinear. Moreover, if the function to perform the BITBLT transfer operation while the transmission coefficient is varied is added, the scale of the conventional image drawing apparatus will be large.
The conventional image drawing apparatus originally does not have means to execute the desired transmission drawing processing as shown in FIG. 2A or FIG. 2B. In order to enable the conventional image drawing apparatus to perform this function, it is necessary that the complicated task to perform the BITBLT transfer operation with the transmission coefficient being varied for every pixel of the image stored in a block area of a memory device be imposed on a CPU of the conventional image drawing apparatus. In such a case, complicated transmission drawing processing must be executed by the CPU, and there is a tendency that the processing time will become very long.